/*************************************************************************
	> File Name: P5708.cpp
	> Author: yufangze
	> Mail: 2224590123@qq.com
	> Created Time: 2024-12-19 16:27:12
 ************************************************************************/

#include <iostream>
#include <set>
#include <map>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
using namespace std;

int main() {
    double a, b, c;
    cin >> a >> b >> c;
    double  p = (a + b + c) / 2;
    double S = sqrt(p * (p - a) * (p - b) * (p - c));
    printf("%.1lf\n", S);
    return 0;
}
